1. Field of the Invention
The present invention relates generally to magnetic recording and/or reproducing apparatus, and more particularly, to an apparatus having a tape guide cylinder and a rotary magnetic head device disposed in the tape guide cylinder and operative to record by the rotary magnetic head a recording video signal on or reproduce by the rotary magnetic head device a recorded video signal from a magnetic tape running on a periphery of the tape guide cylinder.
2. Description of the Prior Art
A video tape recorder which is used for recording a video signal on a magnetic tape or reproducing a video signal from a magnetic tape on which the video signal is recorded is generally equipped with a tape guide cylinder having a periphery thereof providing a running path for the magnetic tape and a rotary magnetic head device disposed in the tape guide cylinder. The magnetic tape running along the running path is applied to wrap around a part of the periphery of the tape guide cylinder at a predetermined wrapping angle thereon. The tape guide cylinder is divided in the direction of its central axis for forming a stationary portion and a rotary portion arranged along the central axis and the rotary portion is rotated at a predetermined speed relative to the stationary portion. The rotary magnetic head device is attached to the rotary portion of the tape guide cylinder to be positioned between the stationary portion and the rotary portion constituting tape guide cylinder with its magnetic gap portion projecting very slightly from the periphery of the tape guide cylinder and rotated with the rotary portion of the tape guide cylinder for scanning with the magnetic gap portion thereof obliquely, the magnetic tape running on the periphery of the tape guide cylinder during each revolution so as to record signals on the magnetic tape or reproduce signals from the magnetic tape on which the signals are recorded.
In recording signals on the magnetic tape by the use of the tape guide cylinder and the rotary magnetic head device described above, a plurality of record tracks are formed on the magnetic tape to be arranged in parallel with one another to extend at a predetermined angle of inclination to the longitudinal direction of the magnetic tape and one field period segment of a video signal is usually recorded on each record track. The rotary magnetic head device which scans obliquely the magnetic tape running on the periphery of the tape guide cylinder during each revolution is operative to record one field period segment of the video signal on the magnetic tape so as to form each of the record tracks during each revolution in a recording operation and to scan the magnetic tape along each of the record tracks formed thereon so as to read one field period segment of the video signal during each revolution in a reproducing operation.
In connection with the video tape recorder, there have been proposed a number of recording and reproducing systems different from one another in specifications of configuration, recording and reproducing operations, operation control and so on. In a kind of standard video tape recorder according to one of these systems, by way of example, the diameter of a tape guide cylinder is selected to be 40 mm, a wrapping angle of a magnetic tape on the periphery of the tape guide cylinder (hereinafter, referred to as tape wrapping angle) is selected to be 180 degrees, the revolving speed of a rotary portion of the tape guide cylinder (hereinafter, referred to as cylinder revolving speed), namely, the revolving speed of a rotary magnetic head device is selected to be approximately 29.97 rps, and the number of rotary magnetic heads constituting the rotary magnetic head device is selected to be two. This standard video tape recorder is included in a group of video tape recorders having a relatively small tape guide cylinder, and the tape guide cylinder and the rotary magnetic head device employed in the standard video tape recorder are referred to as standard tape guide cylinder and standard rotary magnetic head device, respectively.
Apart from the standard video tape recorder aforementioned, there has been also proposed to constitute to constitute a small-sized video tape recorder which is equipped with a tape guide cylinder having its diameter smaller than that of the standard tape guide cylinder and compatible in operation with the standard video tape recorder. Such a small-sized video tape recorder is required, in view of compatibility with the standard video tape recorder, to satisfy the following two conditions:
(1) The length of each record track formed thereby on a magnetic tape coincides with that of each record track formed on a magnetic tape by the standard video tape recorder. PA0 (2) The period of one field period segment of a video signal recorded thereby on the magnetic tape coincides with that of one field period segment of a video signal recorded on the magnetic tape by the standard video tape recorder.
In this connection, assuming that Ra represents the ratio of the diameter of the tape guide cylinder employed in the small-sized video tape recorder to the diameter of the standard tape guide cylinder, Rb represents the ratio of the tape wrapping angle on the tape guide cylinder employed in the small-sized video tape recorder to the tape wrapping angle on the standard tape guide cylinder, Rc represents the ratio of the cylinder revolving speed in the small-sized video tape recorder to the cylinder revolving speed in the standard video tape recorder, it is required for meeting the above mentioned conditions (1) and (2) that the equations: Ra.multidot.Rb=1 and Rb/Rc=1 are satisfied and further that the rotary magnetic head device employed in the small-sized video tape recorder has N (N is an even number larger than two) magnetic gap portions. Accordingly, the small-sized video tape recorder in which the diameter of the tape guide cylinder is selected to be 40 mm.multidot.2/3.apprxeq.26.67 mm, the tape wrapping angle on the tape guide cylinder is selected to be 270 degrees, the cylinder revolving speed is selected to be approximately 44.955 rps, and the rotary magnetic head device with four magnetic gaps portions is employed, may be produced, by way of example, under a condition wherein Ra is determined to be 2/3, each of Rb and Rc is determined to be 3/2 and the number of the magnetic gap portions of the rotary magnetic head device is determined to be four.
In the small-sized video tape recorder thus constituted, since the rotary magnetic head device is required to have four magnetic gap portions, increase compared with the standard video tape recorder, four independent rotary magnetic heads each having a single magnetic gap must be provided if the rotary magnetic head device is composed of plural rotary magnetic heads each having a signal magnetic gap. This raises a problem that it is quite difficult to attach precisely four independent rotary magnetic heads each having a single magnetic gap to the inside of the tape guide cylinder having the small diameter of 26.67 mm. Further, there is another disadvantage that it is also quite difficult to dispose additional rotary magnetic heads used for reproducing the video signal from the magnetic tape in a trick play mode, such as a fast forward reproduction mode (cue reproduction mode), fast reverse reproduction mode (review reproduction mode) or still picture reproduction mode, on the inside of the tape guide cylinder having the small diameter of 26.67 mm, so that a so-called noiseless cue reproduction, noiseless review reproduction or noiseless still picture reproduction can not be obtained.